Explosive detection is an important component of the modern war against terrorism. Explosives may be categorized based on their chemical structure, their sensitivity in certain environments, their decomposition pathway or their general sensitivity to a variety of stimuli.
The UN hazard classification system for classifying explosive materials and explosive components is recognized and used internationally. The UN system consists of nine classes of dangerous materials, with explosives designated as Class 1. The explosives hazard class is further subdivided into six sub-divisions, which are used for segregating munitions and explosives on the basis of similarity of characteristics, properties, and accident effects potential. The six divisions are:
Division 1.1—Substances and articles that have a mass explosion hazard;
Division 1.2—Substances and articles that have a projection hazard but not a mass explosion hazard;
Division 1.3—Substances and articles that have a fire hazard and either a minor blast hazard or a minor projection hazard or both but not a mass explosion hazard;
Division 1.4—Substances and articles which present no significant hazard;
Division 1.5—Very insensitive substances which have a mass explosion hazard;
Division 1.6—Extremely insensitive articles which do not have a mass explosion hazard.
The above classification is further separated into compatibility groups A, B, C, D, E, F, G, H, J, K, L, N and S. For example, group A includes primary explosives and group D includes secondary explosives.
A primary explosive is defined as an explosive that is extremely sensitive to stimuli such as impact, friction, thermal, or electrostatic sources. Primary explosives are sufficiently sensitive that they can spontaneously initiate during “normal” operational activities. As a very general rule, primary explosives are considered to be those compounds that are more sensitive than Pentaerythritol Tetranitrate (PETN), which is considered as a primary explosive in Class 1.1A when it is in dry form, and a secondary explosive in Class 1.1D when it is wetted by at least 15% wt water.
A secondary explosive is less sensitive in comparison to primary explosives and is relatively insensitive to shock, friction, and heat. It may burn when exposed to heat or flame in small, unconfined quantities, and detonation is likely to occur with relatively sensitive secondary explosives. RDX and TNT are two such secondary explosives, so as wetted PETN.
At present, sniffer dogs are considered the most successful, sensitive and widespread tool for explosive detection at airports and in public areas. Detection of explosives by sniffer dogs (or by trained individuals as disclosed in U.S. Pat. No. 6,027,344) has been generally successful where the dog was able to recognize the distinct odor of the specific explosive material. In order for the dog to learn to selectively discriminate the odor of the explosive component from other components, the dog must be brought into intimate contact with the explosive, on numerous prior occasions, and preferably on-site, namely in the perimeter where the dog is assigned to. Under normal conditions, on-site training of sniffer dogs with live explosives is both highly dangerous and typically prohibited.
For primary explosives, training of sniffer dogs utilizing large amount of the explosive, as required by correct training procedures employed in traditional explosives training, is not feasible due to the danger associated with the handling of large quantities of the highly sensitive explosive. Thus, existing training aids for primary explosives are either unavailable in light of the great sensitivity of the primary explosives or limited to employing only minute quantities of the explosive (as low as a few micrograms, which would generally make them of limited reliability).
The detection of a primary explosive, such as TATP, by sniffer dogs has proven particularly problematic for numerous reasons, one of which being the danger the explosive imposes on both the dog and its human trainer and the lack of an appropriate stable simulant material as a training aid, which would have the explosive's distinct odor without the accompanied intrinsic instability.
Apart from the danger in handling large quantities of TATP, the use of powder explosives renders the exposure of the sniffing dog during training to a health problem associated with the entry of powder particulates into its respiratory system, damaging the olfactory cells.
International Patent Application No. PCT/IL2005/000853 (published as WO 2006/021949) discloses a method for the preparation of a non-explosive, homogenous simulant material for simulating hazardous materials. According to the claimed method, the simulant is prepared by obtaining a mixture of at least one explosive material with at least one inert material and mixing said mixture until a homogenous, flexible and non-particulate, paste-like material is obtained.
While the method disclosed in WO 2006/021949 was found effective for the preparation of a vast number of simulants for sensitive explosives, due to the high sensitivity of primary explosives such as TATP the preparation of a suitable simulant material required a different approach.
U.S. Pat. No. 5,648,636 discloses a non-explosive simulant material comprising an explosive and an inert material. While the inventors explicitly list a great number of explosives which may be used, only the more stable explosives have been exemplified, none of which being a primary explosive in general or TATP in particular.